1. Field of the Invention
The present invention relates to a medical television system for producing color and near-infrared images with a single television camera.
2. Related Background Art
A conventional television camera does not have sensitivity in the near-infrared region in order to guarantee color reproduction. In order to produce both near-infrared and color images, a separate camera having sensitivity for the near-infrared region must be prepared. For this reason, the total system results in high cost and is bulky and complicated.
For example, in an intensive care system of FIG. 1, a sickroom is illuminated by an illumination light source 101a of visible light during the day to allow an operator (e.g., a nurse) to monitor a patient P through a color television camera 102a, a control unit 103a, and a color monitor 104. At night, the sickroom is illuminated with a nighttime illumination light source 101b for emitting near-infrared light so as not to interfere with the patients sleep. The patient P is then monitored through a near-infrared television camera 102b, a control unit 103b, and a color monitor 104. Other monitors 104' and 104" are also arranged in the monitor room to allow simultaneous monitoring of patients in other sickrooms. Such a 24-hour intensive care system is used particularly for monitoring patients in critical condition. Therefore, the color television camera 102a, the near-infrared television camera 102b, and their respective control units 103a and 103b must be installed in each sickroom, resulting in high cost.
Japanese Patent Application Disclosure No. 183830/1982 and the like describe apparatuses for projecting a still image of an eye fundus from a nonmydriatic-type fundus camera as a television image. In these conventional apparatuses, a fundus image recorded on a conventional silver chloride film is also displayed on a television monitor to check if the film image is properly photographed.
An example of this type of conventional apparatus is described with reference to FIG. 2. Light from an observation light source 1 of a tungsten lamp or the like illuminates a ring-like opening 4a of a ring slit 4 through a condenser lens 2 and a dichroic mirror 3. As shown in FIG. 3, the dichroic mirror 3 transmits visible light and reflects infrared rays, as indicated by a characteristic curve A. Light through the ring-like opening 4a is temporarily focused near an apertured mirror 6 by a relay lens 5, is focused again near the cornea of an eye E by an objective lens 7 arranged between the apertured mirror 6 and the eye E, and illuminates the eye fundus Ef. Light reflected by the fundus Ef is temporarily focused by the objective lens 7, passes through an aperture of the apertured mirror 6, and is focused near a field lens 10 through a photographing lens 8 and a dichroic mirror 9. The light is then further focused on a light-receiving surface of an image pickup tube 13 through a reflecting mirror 11 and a relay lens 12. The dichroic mirror 9 also has the characteristics given by the curve A in FIG. 3. The fundus image guided to the image pickup tube 13 is displayed as a fundus image Ea on the CRT of a television monitor 14. A film 15 is arranged behind the dichroic mirror 9 through a shutter (not shown). A condenser lens 17 and a photographing light source 16 of a strobe tube are arranged behind the dichroic mirror 3.
The photographing light source 16 is operated during photographing. Visible light from the light source 16 illuminates the ring-like opening 4a of the ring slit 4 through the dichroic mirror 3, and then illuminates the fundus Ef of the eye E through the relay lens 5, the apertured mirror 6, and the objective lens 7. Light reflected by the fundus Ef passes through the objective lens 7 and the apertured mirror 6 and is focused and recorded on the film 15 through the photographing lens 8 and the dichroic mirror 9.
The photographing light source 16 is operated upon operation of the shutter. At the same time, a circuit for producing a still image, as shown in FIG. 4, is operated in response to the shutter signal. The signal from a shutter circuit 21 causes the photographing light source 16 to operate and at the same time is supplied to the image pickup tube 13. An output from the image pickup tube 13 is supplied to an A/D converter 22. The digital signal from the A/D converter 22 is stored in a frame memory 23. The stored data is input to the television monitor 14. The fundus image Ea as the photographed image is monitored on the television monitor 14 so that the photographed image can be checked on the monitor 14. In doing so, the operator can immediately judge whether the image on the film 15 is properly photographed. If it is judged that this is not the case, a necessary countermeasure can be taken immediately. For example, the fundus image can be photographed again.
In the system described above, as is apparent from the characteristics of the dichroic mirrors 3 and 9, since the image pickup tube 13 and the television monitor 14 are, respectively, a monochromatic tube and a monochromatic monitor which have sensitivity to near-infrared rays, a monochromatic still image can be obtained. However, a color still image of the fundus Ef cannot be produced. Another conventional system of this type is known in which flare states on the photographed image are precisely detected so as to allow judgement on whether the image on the film 15 is accurate. According to this system, the dichroic mirror 9 is replaced with a half mirror, the reflecting mirror 11 is set to be movable, as shown in FIG. 2, and a relay lens 12' and an image pickup tube 13' having sensitivity to visible light are arranged behind the reflecting mirror 11. A fundus still image of visible light can be produced by the image pickup tube 13'. In the above system, if the image pickup tube 13' and the television monitor 14 are replaced with a color image pickup tube and a color television monitor, respectively, a color fundus still image can be obtained. However, the system must have two types of image pickup tubes 13 and 13'. The system mechanism therefore becomes complicated and bulky.